Two Sum - LeetCode

题目：

Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

分析：

这道题利用的就是字典查找复杂度为O(1)的快速，避免了暴力查找的长时间。注意的是所给数组中有可能有两个一样的元素，但是字典中不会有重复元素，所以需要特殊处理和判断。

代码：

class Solution:    # @return a tuple, (index1, index2)    def twoSum(self, num, target):        # if not issort(num):            dic ={}            length = len(num)                for i in range(0,length):                dic[num[i]] = i            for i in dic.keys():                if target - i in dic:                    if dic[i] == dic[target - i]:                        pre = num.index(i)                        return pre+1, num.index(i,pre+1)+1                    return min(dic[i]+1,dic[target - i]+1) , max(dic[i]+1,dic[target - i]+1)